1. Field of the Invention
The present invention relates to a magnetic recording medium and a method of producing the same, particularly relates to a magnetic tape medium made by forming a magnetic layer comprised of a metal magnetic thin film on a nonmagnetic supporting body and other metal thin film type magnetic recording media and a method of producing the same.
2. Description of the Related Art
In a magnetic recording field, strong demands have been made on higher-density recording every year along with an increase in the amount of recording information.
In accordance with the above, a magnetic recording medium produced by forming a thin film of ferromagnetic metal by a thin film forming method using plating, vacuum deposition method, sputtering method, ion-plating method and other vacuum thin film forming methods (hereinafter, also referred to as a thin film type medium) has been becoming a main stream instead of those produced by a widely used method of dispersing magnetic crystal grain in a binder to coat (hereinafter, also referred to as a coating type medium).
The thin film type medium having a ferromagnetic metal thin film has excellent coercive force and squareness ratio, etc. and does not require mixing of a binder which is not a magnetic material in its magnetic layer as in the coating type medium, so it is possible to heighten the filling density of a magnetic material (in other words, a magnetization amount per unit volume) and to make a film thickness of the magnetic layer remarkably thin compared with that of the coating type medium. Thus, it has an excellent electromagnetic conversion characteristic in a short wavelength range expected to be broadly used in the future.
Furthermore, the above thin film type medium has a characteristic that its recording degauss is remarkably small.
From the above advantages, the thin film type medium having a ferromagnetic metal thin film will be a main stream in magnetic recording media for high-density recording in the future without doubt.
In a magnetic recording system using a magnetic recording tape, a kind of thin film type media, so-called obliquely evaporated tape has been put into practice so as to improve electromagnetic conversion characteristic and attain a higher output in the short wavelength range.
FIG. 1 is a cross-sectional view of the above obliquely evaporated tape.
A magnetic layer 3 as a ferromagnetic metal thin film is formed on a nonmagnetic supporting body 1, a protective film 4 made of carbon, etc. is formed thereon, a top coat layer 5 made of lubricant, etc. is formed thereon.
On the other hand, a back coat layer 6 is formed on the back surface of the nonmagnetic supporting body 1.
The magnetic recording medium having the above configuration is cut to be a tape shape to form the obliquely evaporated tape.
The nonmagnetic supporting body 1 is comprised of a high polymer film such as a polyester film, polyamide film, polyimide film, etc.
The magnetic layer 3 is a ferromagnetic metal thin film formed by the so-called oblique evaporation method of moving the nonmagnetic supporting body 1 in a predetermined direction and depositing a magnetic metal on the surface of the nonmagnetic supporting body 1 from an oblique direction by a vacuum deposition method.
As the magnetic metal composing the above magnetic layer 3, Co and Ni are widely used.
To form the above magnetic layer 3 on the nonmagnetic supporting body 1 by the vapor deposition method, a method of using, for example, Co and Ni as a vapor deposition source and spraying an oxygen gas to the moving nonmagnetic supporting body is widely used.
When forming a film as the above, the magnetic layer 3 becomes to have a configuration in which magnetic crystal grain of α-Co (or Co—Ni) and nonmagnetic CoO (or CoNiO) exist together.
Here, an object of introducing oxygen into the film is to improve magnetic characteristics by introducing nonmagnetic crystal grain and making crystal grain finer and to reduce medium noise by interrupting magnetic bonding between magnetic crystal grain.
In the thus obtained obliquely evaporated tape currently in practical use, an inclination angle of an easy axis of magnetization of the magnetic layer 3 is about 20 to 30°.
Since magnetic crystal grain is oriented obliquely with respect to the surface of the nonmagnetic supporting body in the magnetic tape produced by the above oblique evaporation method, higher-density recording becomes possible compared with magnetic tapes of the related art wherein magnetic crystal grain is oriented in the longitudinal direction of the supporting body of the tape shape.
In the fields of VTR and computer storage, however, a tape having a larger capacity, more compact body and lighter weight by further higher-density recording are desired for the above obliquely evaporated tape.
To realize higher-density recording than that of currently used magnetic recording tapes, a higher output and lower noise of the medium, that is, a higher C/N ratio is essential, particularly, a higher C/N ratio in the short wavelength range is significant.